Microphone



M y 1944- I F. c. BEEYKLEY 2,350,010

MICROPHONE Filed Dec. 26, 1941 GACKGEOUNO Patented May 30,1944-MICROPHONE Francis Cheyney Beekley, West Hartford, Conn., assignor to.The Glastonbury Bank a Trust Company, Glastonbury, Conm, a bankingcorporation of Connecticut. as trustee Application December 26, 1941,Serial No. 424,43?

.16 Claims.

This invention relates to means responsive to sound for creatingelectricv pulses, such as a microphone adaptable for use in radiobroadcasting, radio and wire-telephone, communications, signaling, orpublic address systems.

' In electricalltransmission of sound, it is desirable to eliminatebackground noises to assure clarity and'substantially perfecttransmission or the speech, music, or other sounds which constitute thematerial intended to be transmitted. This is accomplished in radiobroadcasting, for instance, by locating microphone and performer in asoundproof studio. 'l'here are, however, many cases where it isimpracticable to locate a microphone in an enclosure properlysoundproofed against extemalnoises and intemal reverberation. Examplesof thi include radio broadcasting of sports events and conventions andpolitical gatherings, public address systems, military and othercommunications. where transmission must be made from noisy locations orreverberatory enclosures.

I cancellation of the background noises and the nai The primary objectof this invention is to pro-' vide a microphone which may be used in anoisy or reverberatory. location. which microphone will automaticallycancel out all or a material portion of the backgroundnoise and therebypermit transmission of speech or other desire sounds having acceptablefidelity.

A further obiectis to provide a microphone with vibrating means soarranged therein as to illustrating a .diflerent electrical connectionbe-f I tween two sound-responsive units of the carbon granule type;

Fig. 4 is a diagrammatic view or a device the ing two sound-responsiveunits of the. magnetic type: v

Fig. 5 is a diagrammatic view illustrating the ture of the excitationwaves of the microphone;

Fig. 6 is a cross sectional view of still another embodiment of theinvention;

Fig. 7 is a perspective view of one form which the Fig. 6 embodiment maytake; and

Fig. 8 is of Fig. '7.

Referring to the drawing, and particularly to Figs. 1 to 5, inclusive,which illustrate one em.- bodiment of the invention, the numeral illdesignates a base plate having an elongated form bent centrally at II toprovide two angularly disposed end portions l2. 'ljhese end portions arepreferably oi a size and shape to have mounted thereon two casingportions whose axes exten perpendicular to the plane of the face of theplate Portion I2 upon which each is mounted. The

- faces I of the casing portions "have openings therein and are disposedin the same angular-replation that the plate portions I! bear to each beadapted to receive background noisesi'rom all:

directions in counterbalancing or cancelling relations. applied theretointentionally in an unbalanced relation.

tion: such microphone actuable only by. vibra- A further object is toprovide a microphone which is substantially unafl'ected by noisesoriginating from any point at a distance and adapted to be excited onlyby vibrations originating close by and in properly directed relation.

A further obiectis to provide .a microphone 'with diaphragm meanssubject to e'xcitation in counterbalancing or cancelling relation, byvibrations originating at a distance therefrom and in any angularrelation to.

Other objects will be apparent from the drawing and appended claims.

Inthedrawing:

Fig. 1 is a side elevation of'one embodiment of the invention:

. Fig. 2 is a diagrammatic view oi an embodiment of the inventionutilizing two sound-responsivli uiinitsoithecarbougranuletypep 21 whichmay 3 is a diagrammatic view of the invention 58 other, namely, inobtuse angled relation. An electrical conductor I5 projects from thebase ll 1 and is connected with the microphone.

'I'he'mlcrophone further includes vibrating 'means including difierentsound-receiving portions spaced in close relationship, such as thediaphralgms. It and I1 (see Flg. 12) each of which may be located withinone or the casings I 4. Associated with each diaphragm is an electricalmeans 1 including a button or housing I. separated there 7 asectional'view taken on line 8-1 from by a felt washer l9; said housingbeing filled with a plurality oi loosel arranged small carbon granules20. Diaphragm II is electrically connected by conductor 2!, in which maybe interposed a battery 22, with one end of the primary coil 23 01 atransformer. The opposite end of said coil is connectedby conductor-'24with the button associated with diaphragm I. A com .ductor 25 connectsthe button I l associated with diaphragm ll with a second primarytransformer coil 2 at the end of is connected. The

pposlteendof coil flisconnected with di phragm ll by mean of conductorhave battery 28 interposed there'- in. The coils II and it constituteseparate primary coils of a suitable transformer having cores the coilli'complementaryj to the end of coil 23. with which conductor 2! 29 and30 associated with coils 23 and 2t resmctively, and having a singlesecondary coil ti associated with both cores. The two diaphragm unitsare connected to the transformer primaries in opposite orcounterbalanc'ing relation.

Referring to the Fig. 3 construction, two diaphragm units, each housedin a casing portion 53, are connected in counterbalancing electricrelationship. 'lhus, diaphragm 32 is connected by conductor 33,including a battery it, with the j primary coil 35 of one transformer.The other end of coil 35 is connected.by conductor 3% with the button 3iassociated with diaphragm 32. lihe other diaphragm 38 is connected byconductor 39, which has battery 5i interposed therein, with. one end ofprimary transformer coil it. ll'he other end of coil it is connected byconductor M with the button 62 associated with diaphragm 38. Thetransformer of which the coil 35 con stitutes the primary has a core 33and a secondary coil M. The transformer of which the coil tilconstitutes the primary has a core tdand a secondary coil tit. Aconductor i'l connects adjacent ends of the transformer secondary coilsat and t6, and a line dt-connects the opposite ends of transformersecondary coils dd and it. Lead line 49 is connected with line at andlead line 50 is connected with conductor at.

In the embodiment illustrated in Fig. a, dia phragm has a coil 55connected therewith. A permanent magnet 51 is associated with diaphragm55 and carries two pole pieces 55 adjacent its ends and each extendingadjacent opposite sides of coil 56. Another pole piece 5%! is carriedcentrally by magnet 51 and extends within coil 56. The two unitsemployed in the Fig. embodimentare of similar construction, and likeparts bear the same reference numerals. A conductor 5i connects one endof one coil 56 with the opposite end of the other coil 56, and aconductor 62 connects other ends of the two coils 56. Leads G3extendfrom conductors 6i and 52.

Each of the Figs. 2, 3, and 4 embodiments is operable for the intendedpurpose of cancelling out background noises and transmits only properlydirected vibrations emitted in close spaced relation to one diaphragm ormembrane when the two following requirements are met. These tworequirements are: first, that the diaphragms placed substantially 180"so that they will fully counterbalance each other. Whenthese tworequirements are satisfied in any of the aforementioned embodiments, theoutput of each unit will be that represented diagrammatically in Fig. 5,wherein the output from one unitin reference to background noises willbe represented by one of the dotted wave lines, while the output of theother will be represented by the'other dotted wave line. Note that thesewave lines are in counterbalancing relation and hence will cancel outand eliminate background or ambient noises. The full line in Fig. 5represents the signal wave produced by the one unit against whichvibrations are directed from a close spaced emission point. As usedherein, the, term- "ambient". when referring to sounds or noises will beunderstood to mean unwanted surrounding sounds or noises, i. e. externalsounds or noises not desired to be transmitted.

assume in the use or the microphones described above, it is essentialthat thevibrations constituting the signal to be transmitted shall beemitted at a point spaced close to and directed toward one only of themembranes or diaphragms, so as to reduce to a minimum the efieco oi thesignai upon the other diaphragm. This avoids the cancelling effect whichactuation or" the other diaphragrn will have on the intended signalingvi oration. In this connection, tests of units eznbodying theaters-saidinvention, and particu larly the d embodiment, show that, whereassignals tr itted from a conventional micron a military tank while thattanl: e have a poor percentage of the use of a microphone embodying ionswith respect to volume and character of bacliground'noise produce agreatly in= creased degree of intelligibiiity. Fence, a neicro phoneconstructed according to "event-ion overcomes very serious obstaclesheretofore en countered in radio transmission, especially for militarycommunications, and raises the percentage of intelligibility overadverse conditions to an extent which reduces materiaily the possibilitythat signals will be misunderstood or undecipherable at the receiver.While twoseparate casing portions have been shown and described,

' it will be understood that this is illustrative only,

- which is so arranged that it is balanced with intermediate the polepieces 12.

relation to both of the openings ti and as and divides housing 65 intotwo chambers or sub stantially the same size and shape. Therefore, ifvibrations or sound waves are applied equally at the housing openingsEL-td, they will act equally and oppositely upon the diaphragm iii toprevent vibration thereof. A magnet "H hat/- mg pole pieces '32 iscarried by housingttat one side of diaphragm l0, and a pole piece it iscarried centrally of magnet Ii and positioned A coil Hi is connected tothe diaphragm in a well known manner. It will be observed that when thesound waves constituting a signal are emitted in close spaced relationto and are directed into one oi the openings 61-68, the diaphragm it wil be caused tovibrate, and hence to actuate the elec tromagnet portionof the microphone to trans unit the intended signal.

The embodiment illustrated in Figs. 7 and it, a variant of theembodiment illustrated in 6, has been found efllclent in operation. Inthis embodiment, cylindrical housing d9 having plane parallel endmembers at has diaphragm or vi brating member 82 mounted centrallybetween and parallel to the end walls 8|.

A button 83 confines carbon granules and leads 8t and lit extend fromthe diaphragm t2 and the button 83. The cylindrical body portion of thehousing 83 has a pair of openings 8? formed therein. These openings arepreferably elongated'and equally spaced to either side of the diaphragm82, whereby the opposed surfaces of the diaphragm constitute spacedsound-receiving portions. These openings 81 are spaced apartcircumferentially a small distance, preferably not greatly in excess ofinch and hence only a small fraction, i. e., not exceeding one fourth,of a wave length of sound of the highest frequency which it is desirableto cancel. It will be observed that sound waves entering these twoopenings 81 will act equally and oppositely upon the diaphragm 82.whereas sound waves applied in close spaced relation to one only of theopenings Bl as indicated by the arrow in Fig. 3 will vibrate thediaphragm 82 to actuate the microphone. In practice, such application ofa spoken signal intended for transmission is accomplished by speakingdirectly into one only of openings 81 while the microphone is held inclose spaced relation to or even in contact with the lips of the user.

It will be observed that each of these embodiments of the inventionemploys the principle of automatically counterbalancing within themicrophone sound waves impressed in balance at two spaced portions ofthe microphone. This counterbalancing cancels any unwanted signal orvibration which normally would excite a microphone positioned in a noisylocation. These two portions may constitute either the two .diaphragmsin the embodiment of Figs. 1 to 4 or the opposite faces of a singlediaphragm in the embodiment of Figs. 6 to 8. At the same time, anannouncer may speak into .the microphone or cause selected signals to beemitted in a selected direction and at close spaced relation to themicrophone for the purpose of causing its operation to transmit thedesired signal substantially without interference from backgroundnoises. The effect is produced when the device is properly constructed,and the only care required is to insure proper direction and emission ofthe sound waves which are to constitute the intended signal so thatthere will be' a difference in either amplitude or phase of the sound reoeived at the two portions of the microphone aforementioned.

I claim as my invention:

waves to said directing means for unbalanced impression thereof on saidvibrating means.

4. A microphone comprising diaphragm means, means spaced apartapproximately three eighths of an inch for normally directing ambientsound waves for impression upon two surfaces of said vibrating meanssubstantially in phase, and electrical means adapted to be energized bysaid diaphragm means, said electrical means transmitting a signal inresponse to sound waves-impressed on said diaphragm surfaces inunbalanced relation only.

5. In a microphone, vibrating means, electrical means responsive to saidvibrating means for transmitting a signal, and means arranged to permitambient sound waves to impinge upon said vibrating means at spacedpoints substantially in phase and in substantially equal amplitude sothat they oppose and substantially cancel out their combined eflect.

6. A microphone comprising vibrating means, means for housing saidvibrating means, said housing means having a pair of openings in com- 1.A microphone comprising vibration means having two non-directionalsound-receiving portions, spaced apart a small fraction ofa wave lengthof audible sound for normally equal impression of sound thereon, andelectrical signal means responsive to said vibration means, saidelectrical means being rendered operative to transmit a signal only whensound is impressed I derantly'against one of said points.

3. In a microphone, vibrating means, means spaced apart not more thanone fourth wave length for directing sound waves originating at adistance for impression upon said vibrating means in substantiallyidentical phase and amplitude, and electrical means responsive to saidvibrating means and actuable to transmit a sig-- nal only uponunbalanced application of sound plementary relation to said vibratingmeans for passage of sound waves to impress said waves on said vibratingmeans at spaced points in substantially identical phase and amplitude,and electrical means responsive to said vibrating means for transmittinga signal only when sound waves are emitted in close spaced relation toand directed at one opening.

'7. A microphone comprisin vibrating means having two sound-responsivesurfaces, electrical means associated with said vibrating means, andmeans spaced apart less than one inch for directing sound wavesoriginating at a distance from said microphone and from any or alldirections to impress said waves upon said two sound-responsive surfacesin substantially identical phase and amplitude, said electrical meansbeing actuable to transmit a signal only when sound waves are unequallyapplied to said two sound-responsive surfaces.

8. A microphone having a casing, and a diaphragm in said casing, saidcasing having a pair of openings in complementary relation to saiddiaphragm for exposing the opposite faces of said diaphragm to equalcounterbalancing impact by ambient sounds originating at a distance fromsaid microphone.

9. A microphone comprising housing means including two complementaryindependent chambers each having an opening, vibrating means havingspaced portions each exposed at one chamber, and electrical meansresponsive to said vibrating means, said openings being close spaced andarranged in complementary relation to said vibrating portions, saidelectrical means being actuable to transmit a signal only uponunbalanced reception of sound in said chambers.

10. A microphone comprising a pair of diaphragms having substantiallyequal characteristics of vibration, means fixedly mounting saiddiaphragms in juxtaposed relation, and electrical means energized byeach diaphragm, said electrical means having a counterbalancing phaserelation.

11. A microphone comprising a pair of matching non-directionaldiaphragms, a mounting securing said diaphragms in fixed relation spaced9. small fraction of a wave length of audible sound, and electricalmeans responsive to each diaphragm, the phase angles of said electricalmeans being displaced.

12. lA microphone comprising a pair of nonwaves substantially in phaseand equal amplitude, the electrical means of sai units being;connected-180 out of phase.

13. A microphone including a pair of vibrating membranes, said membraneshavin matching vibration characteristics, and means for counterbalancingequal components of vibration impressed simultaneously on bothmembranes.

14. A microphone comprising a housing having a pair of similar openingsspaced apart less than one-fourth of a wave length of sound of thehighest frequency of any selected portion of the audio frequency range,a vibrating membrane mounted in said housing in complementary relationto and between said openings, and electrical means associated with andresponsive to vibrations of said membrane.

15. A microphone comprising a housing having a pair of similar openingsspaced approximately three-eighths of an inch, a vibrating membranemounted in said housing in complementary relation to and between saidopenings, and electrical means associated with and responsive tovibrations of said membrane.

16. A microphone comprising a housing, a vibrating membrane mountedsubstantially centrally in said housing, and electrical means associatedwith and responsive to vibrations of said membrane, said housing havinga pair of close spaced divergently facing similar openings therein onopposite sides of and in complementary relation to said membrane.

FRANCIS CHEYNEY BEEKLEY.

